Yamato Transport Co., the nation's leading door-to-door parcel delivery provider, plans to raise its base shipping fees by the end of September for the first time in 27 years, company sources said Tuesday.

The rate hike is aimed at maintaining service quality as the firm faces insufficient manpower, including van drivers, amid an increase in online shopping and struggles with growing costs for outsourcing a part of its deliveries, the sources said.

The group firm of Yamato Holdings Co. has already begun talks with major clients, including Amazon.com Inc.'s Japan unit, over the envisioned fee increase, they said.